1. Field of the Invention
The present invention relates to power regulators, and more particularly to a power controller with an improved voltage tracking reference to prevent latch up without compromising inrush current.
2. Description of the Related Art
The power supply requirements of various chipsets include specific sequencing to prevent latch up. One type of requirement is known as ratio-metric tracking, in which the output of the power converter tracks the voltage of the main supply rail up to a desired point, and then begins regulation at that voltage level. In many conventional tracking configurations, the tracking input was coupled directly to the compensation loop of the power controller chip, such as via an additional input of the error amplifier. In such configurations, a relatively large change in voltage per unit time (DV/DT) of the main supply rail was otherwise coupled directly via a proportionate tracking voltage to the compensation loop via the error amplifier. Without compensation, such tracking voltage variations potentially caused large jumps in output voltage, which otherwise requires a large amount of input current. Such “inrush current” can potentially cause the input supply to collapse or cause damage to components on the board.
Conventional tracking configurations added an RC filter or the like to the input of a tracking reference to prevent noise injections and some moderate DV/DT disruptions. In the conventional configurations, excessive DV/DT disruptions still posed a threat of compromising inrush current specifications, resulting in output regulation disruption and even latchup and malfunction or damage. Any high frequency noise on the tracking reference pin could directly enter the error amplifier and cause disruption of the output regulation. Further, the conventional designs required at least an extra capacitor to filter the tracking reference pin.